Electric image development



July 21, 1959 Filed Dec. 2l, 1953 FIGI INVENTOR.

CLYDE R MAYO BY i" NEGATIVE POLARITY HIGH VOLTAGE SOURCE ATTORNEY July2l, 1959 c. R. MAYO ELECTRIC IMAGE: DEVELOPMENT 2 Sheets-Sheet 2 FiledDec. 21, 1953 mmlll mUDOW IN V EN TOR.

CLYDE R. MAYO ATTORNEY United States Patent O ELECTRIC IlVIAGEDEVELOPMENT Clyde R. Mayo, Rochester, N.Y., assigner, by mesueassignments, to The Battelle Development Corporation, Columbus, Ohio, acorporation of Delaware Application December 21, 1953, Serial No.399,293

4 Claims. (Cl. 117-175) This invention relates in general to a methodand apparatus for development of an electrostatic image, and inparticular relates to an improved method and apparatus for thedeposition of visible powder material on an electrostatic image inconformity with an image such as, for example, the development of aXerographic image or the like.

In Xerography it is usual to form an electrostatic image correspondingto a pattern of light and shadow to be recorded, and to develop thisimage or make it visible by deposition of electroscopic materialthereon. Most simply and directly, a photoconduotive insulating layer iselectrically charged and exposed to a light pattern whereupon the chargeis selectively dissipated to yield an electrostatic charge pattern onits surface, this charge pattern generally being called an electrostaticlatent image. In order to utilize this latent image in the production ofa visible print, it ultimately is desired to deposit visible material inconformity with the image. One method of accomplishing this result isdisclosed in Wise Patent 2,618,552 in which a two-component developermixture is cascaded or rolled across an image-bearing surface to depositpowder particles in conformity with the image, while other systems such`as those disclosed in Carlson U.S. 2,297,691 employ sprayed dustparticles or other means or methods for deposition on lthe electrostaticlatent image. These various systems of development have their relativemerits and disadvantages. For example, the cascading system is quick andeasy and is well adapted to the formation of dense black images of highcontrast. However, it gives rise to problems in maintenance of properrelative proportions of the two components during prolonged operationand gives rise to many mechanical problems in feeding the two-componentdeveloper to the image-bearing surface.

Now, in accordance with the present invention, there are provided means,methods, and mechanisms for the development of an electrostatic latentimage whereby powder particles or the like are carried to animage-bearing surface by a support layer such as a web, sheet or thelike and are deposited thereon in conformity with said image to yield aprint of excellent quality. The invention is particularly well suited toXerography in that it is inexpensive, convenient, and well adapted toautomatic operation.

The general nature of the present invention having been set forth, therewill now be presented a more detailed description in illustration butnot limitation on the invention in the following specification anddrawings in which:

Fig. 1 is -a diagrammatic side cross section of an insulating surfacesupporting an electrostatic latent image;

Fig. 2 is a diagrammatic side cross section of developing rice mechanismfor developing the image illustrated in Fig. l,

Fig. 3 is a diagrammatic side cross section of an imagebearing memberand development member immediately after development has taken place;

Fig. 4 is a diagrammatic side cross section of a development memberaccording to one embodiment of the invention;

Fig. 5 is a diagrammatic view of development mechanism according toanother embodiment of the invention; and

Fig. 6 is a diagrammatic view of an automatic xerographic machineaccording to the present invention.

The present invention is particularly intended and adapted for thedevelopment of an electrostatic latent image, such as particularly alatent image of relatively iine detail composed of relatively chargedand uncharged areas on an insulating surface. Such an image may, forexample, be an electrostatic latent image corresponding to a pictorialsubject such as a conventional photograph, snapshot, or the like, or maybe an electrostatic latent image corresponding to a document,manuscript, or other representation of infomation to be reproduced.Images of this sort, and other images requiring an optical resolution inthe order of about ten lines per millimeter or better, form the usualsubject of development according to conventional Xerographic systems.

illustrated in Fig. 1 is such an image system, presenteddiagrammatically, comprising a Xerographic member generally designated10 consisting of a conductive backing member 11 and an insulating layer12 thereover, which insulating layer desirably may be a photoconductiveinsulator. On or near the surface of the insulating layer 12 is anelectrostatic image designated by the plus marks 14 at the surface ofthis layer. lt is to be understood that the electrostatic latent imagemay be of either positive or negative polarity and may consist ofgradations of potential or charge or may be, as illustrated in thefigure, areas of charge interspaced by arcas of substantially no charge.The particular image illustrated in Fig. 1 may be regarded `as a linecopy image consisting of respective areas of charge and absence ofcharge which desirably can be printed as areas of black on a whitebackground.

In Fig. 2 is shown, diagrammatically, developing means and apparatussuitable for developing the image illustrated in Fig. 1. Thus, forexample, there is shown an insulating layer 12 having electrostaticimage areas 14 on one surface thereof. For this reason, dispo-sed overthat insulating layer is a development member being a sheet or webgenerally designated 15 consisting of a sheet or web of a supportmaterial 16 such as a sheet of pape-r, plastic, cloth, metal such asaluminum foil, metal-backed paper, or the like, on one surface of whichis a loosely adhering coating of electroscopic material 17 consisting offinely divided powder particles electrostatically adhering to thesurface of the support member 16. These powder particles may be anysuitable xerographic toner material, this being generally a finelydivided powder material which is visible against a printing surface,such -as a surface of paper' or the like, and which is electrostaticallyattractible to an electrostatic latent image. It may, for example,consist of finely divided pigment particles or finely dividedcompositions of colored or pigmented resins or the like such as are wellknown to the tart of Xerography. Positioned and disposed at the reverselside of the development member or web 15 is a contact member such as aroller 13 or the like adapted to bring the development member uniformlyagainst the image-bearing surface. This contact member serves to achievesubstantial contact between the development member and the imagesurface, and it is presently believed that pressure is unnecessaryexcept to the extent needed to assure `good contact. Desirably, thecontact roller or like may be movable across the surface so as to bringthe development web or sheet into contact at all portions of theimage-bearing surface and thus, for example, the roller 1S is rotativelymounted on a handle 19 and is adapted be rolled across the entiresurface.

Fig. 3 is a diagrammatic illustration of a mechanism of the developmentprocess illustrating the image-bearing surface 12 and the developmentmember 15 after development of the electrostatic image has beenaccomplished. It is observed at this stage that a portion of the powderparticles 17 originally residing on the development member 15 has beentransferred to form an image body Ztl on the image-bearing surface. Ingeneral, the powder particles may be regarded as being oppositelycharged with respect to the polarity of charge on the image-bearingsurface so that these powder particles are loosely secured to theimage-bearing member by means of the electrostatic attraction betweenthese particles which may, for example, be negatively charged and theelectrostatic latent image which in this same example would bepositively charged.

Fig. 4 illustrates a specific embodiment of a development memberaccording to the present invention wherein the development member,generally designated 15, comprises a `support sheet or web 21 havingcoated or impregnated thereon a coating or layer 22 with a tonercomposition 17 loosely adhering to the coating 22. According to thisfigure, the support member 21 may be a sheet or web of paper,cellophane, or other sheet or web-like material including plasticsparts, self-supporting resin films and the like, and is adapted to be astructural support for the development member and preferably astructural support which is repeatedly exible. Impregnated or coated onthe surface of the structural support is a suitable resin film to form atoner support body on at least one surface.

The coating 22. on the support member 21 may be any of a number ofcoating or impregnating compositions carefully selected with referenceto the nature of the toner particles in the powder layer 17. With anyparticular powder composition selected for the powder layer, and for aparticular type of electrostatic image to be derveloped, a specific andparticular coating or impregnating composition should be chosen in orderto give superior results. Thus, for example, there may be selected adeveloper composition such as is disclosed in U.S. Patent 2,659,670 andin conjunction therewith there may be used as a coating composition aresin material such as is disclosed in U.S. Patent 2,618,551 as acoating composition for a carrier bead or the like. A coatingcomposition of the type selected will be applied to the support sheet orweb by coating, impregnating or like methods. In general, better resultsare achieved with such coated sheets and good development has beenrecorded with coated metal foil, paper of both clay-coated and noncoatedbases having the carrier coating thereon, cloth such as nylon and thelike with the carrier coating, and other sheet-like members as shown inthe figure.

Various coating compositions may be used depending on whether positiveor negative polarity images are being developed and depending on thetoner or powder employed. For example, in U.S. Patent 2,659,670 there isdisclosed a toner comprising a pigmented, modified phenol formaldehyderesin, which toner is commercially available under the name XeroX toner.User in conjunction with this material such coating compounds aspolyvinyl resins, acrylic and methacrylic resins, cellulosicderivatives, and protein materials will, in general, form a coating toimpart negative charge to the toner upon triboelecn'ic contact. On theother hand, asphaltum powder d in combination with coatings such aspolystyrene will tend to provide positively charged powder particles.

The layer of powder material 17 on the development member 15 ischaracterized by being loosely adhering and by being `secured to thesupport sheet or web substantially exclusively by electrostaticattraction. In general, this layer of powder is applied to the supportmember prior to its use as in development by application of the powderto the support member with mild frictional action. For example, asuitable support sheet of uncoated or coated paper, plastic or the likeis treated with a powder composition by brushing the powder onto thesurface of the support member with a camels-hair brush or the like.Thus, the powder layer is readily applied to the paper or like surface.Alternatively, a layer of powder may be shaken across or onto thesurface of the support member or may be applied from a rotating brushbearing a quantity of the toner composition, or by passing the supportmember into or through a body of such toner composition. In the case ofa porous support such as a sheet of paper, a highly desirable method forapplying the powder to the surface is by blowing through the pores ofthe member a stream of air carrying a suspension of the tonercomposition. Other methods of depositing the powder layer on a supportmember will be obvious to those skilled in the art. For example, apowder layer formed on a sheet or web in any desired way may be chargedby corona discharge or other ion deposition. Likewise, a two-componentxerographic developer as described in U.S. 2,638,416 may be cascadedacross a sheet or web, preferably with excess powder or toner, to form adense deposit of charged powder thereon.

It is to be understood that either positively charged or negativelycharged powder may be coated on the developA ment member. Desirably, thesurface of the member then should be of opposite triboelectricrelationship to the powder. Thus, for positively charged powder, thedevelopment member surface should be negative with respect to thepowder, and where the layer is coated by cascading, as just described,the granular carrier of the two-component system likewise should benegative with respect to the powder.

In Fig. 5 is illustrated another apparatus and mechanism for developmentaccording to the present invention. According to this embodiment, anelectrostatic latent image support 12 is developed by means of adevelopment member 15 comprising a support sheet or web 16 and a powderlayer 17 with a corona discharge electrode 25 connected to a negativepolarity high voltage source 26 and adapted to be passed across thereverse surface of the development member 1S. The development sheet isplaced with the powder side against the image-bearing surface 12 andcorona electrode 25 is passed across the surface, causing coronadischarge from the electrode to charge the development member 15 andsecure it firmly against the image-bearing member 12. When thedevelopment member is stipped from the image surface, it is found that asubstantial portion of the powder has been transferred to the imagesurface in the image areas thereof.

In Fig. 6 is illustrated a continuous machine adapted to form axerographic print on a sheet or web member following upon exposure to asuitable light source or other source of a pattern of light and shadowto be recorded. A cylindrical support 41 is mounted on an axle 42 withdrive means comprising a belt 43 operating on pulley 44 from a drivemotor or the like 45. The surface of cylinder 41 is coated with aninsulating image-bearing surface comparable to surface 12 of Fig. 1 orone or more of such image-bearing surfaces are mounted on a cylindersupport. In the embodiment specifically illustrated in the ligure, it isto be understood that the apparatus is designed to reproduce from apattern of light and shadow in which case the image-bearing surfacecorresponding to surface 12 of Fig. l is a photo-conductive insulatingsurface adapted to receive and retain an electrostatic charge and todissipate this charge upon exposure to light. Y

Positioned adjacent to the path of motion of the surface of the cylinder41 is a charging station 47 comprising, for example, a positive polaritycorona discharge electrode consisting of tine wires suitably connectedto a high voltage source 48 of potential hi-gh enough to cause a coronadischarge surrounding the wires. Subsequent to the charging station 47in the `direction of rotation of the cylinder is an exposure station 49generally comprising suitable means for imposing a pattern of light andshadow on the surface of the cylinder and including, for example, aprojection lens 50 or other exposure mechanism as is conventional in theart, preferably operating with slit projection methods to focus a moving`image at an exposure slit 51.

Next subsequent to the exposure station is a developing stationgenerally designated 52 as will be further described hereinafter. Beyondthe development station 52 is a suitable transfer station 53 adapted totransfer a xerographic image from the surface of the cylinder to atransfer web 54 which passes from a feed roll 55 into contact with thecylinder surface at a point lbeneath a transfer electrode 56 anddesirably subsequently through a fusing or fixing device 57 to 1atake-up roll 58. Desirably, electrode 56 is a corona discharge electrodeoperably connected to a high voltage source 59 of like polarity withrespect to high voltage source 48 whereby an limage body deposited onthe cylinder surface is transferred to the transfer web. Fusing device57 permanently fixes a transferred image on the web to yield a completedXerographic print.

Optionally, a cleaning station 62 may be disposed adjacent to thesurface of cylinder 41 along with other auxiliary devices or stations orthe like, whereby residual powder image, electrostatic charge or othermaterial or phenomenon may be cleaned or erased from the cylindersurface. Thus, for example, a rotating brush 63 driven by motor 64through belt 65 may be brought to bear against the surface of thecylinder to erase residual powder image therefrom, or further chargingmeans, oodlight means 0r the like may affect electrical or photoncontrolled operations.

At the development station, las illustrated in Fig. 6, is a developmentbelt passing around roller 67 which is disposed and positioned to bringthe belt 15 to rm contact with the surface of cylinder 41. The belt 67also passes around a drive roller 68 and a guide roller 69. Desirably,drive roller 68 is driven by a motor or other drive means 70 operatingthrough belt 71, preferably to drive the belt in the same direction asthe surface rotation of cylinder but at a speed substantially in excessof the speed of rotation of such cylinder. Thus, there is maintainedbetween belt 15 and cylinder 41 a sliding contact which serves the dualpurpose of insuring extremely quick contact between all points of thesurface of cylinder 41 and the development belt, -and further bringingto each point of the cylinder surface a subsubstantially greaterquantity of the powder layer than is carried by any one point of thedeveloper belt.

Adjacent to one portion of the path of motion of the developer belt 15is a powder-loading station which may, for example, comprise a developerhopper 74 containing a supply of developing powder, preferably as mixedpowder and carrier developer. This hopper opens against the developmentweb or belt 15, whereby the belt passes in contact with the developersupply and is coated with powder as the belt passes upwardly against thedeveloper. Other belt loading mechanisms may, of course, be substitutedfor the one shown herein.

In operation of the invention in general, a xerographic electrostaticlatent image or like electrostatic latent image is formed on animage-bearing surface 12 and the development member 15 is placed againstthis surface. Firm contact between the development member 15 and imagesurface 12 is obtained, for example, by means of roller 18 of Fig. 2 orroller 67 of Fig. 6, or other like device or mechanism. After the entiresurface of the development member has been brought into contact with theelectrostatic latent image-bearing surface, the development member isremoved from the surface leaving an image body deposited thereon. Thisimage body is utilized as may be desired, and in Fig. 6 is illustratedthe utilization of this image body by transfer to a transfer webfollowed by fusing or permanent fixing of the image body in its`configuration thereon.

The operation of the invention according to the device of Fig. 6 isgenerally in accord with the operation as applied to all gures. Thus,for example, a xerographic photosensitive member on the surface ofcylinder 41 is carried past the charging station wherein anelectrostatic charge is applied to theV photosensitive member. Accordingto present commercial xerographic operations, this surface charge is ofpositive polarity. The cylinder then rotates to bring the chargedsurface to an exposure station Where a pattern of light 'and shadow tobe recorded is imposed on the surface of the charged xerographic member,and the charge is thereby selectively dissipated to leave anelectrostatic latent image. The image-bearing surface then passes to thedevelopment station where it is rmly contacted by development member 15.As the process continues, development member 15 constantly passesthrough the loading Zone wherein additional toner or powder is appliedto the surface of the support member, and this reloaded surface iscontinuously again brought into contact with the surface of cylinder 41.The relative speed of motion of belt 15 and cylinder 41 may be variedaccording to the individual needs and purposes. Thus, for example, thetwo surfaces may be in synchronized motion whereby substantially noslippage occurs. However, it has been found, surprisingly enough, thatsliding motion has certain advantages, chief among which are theincreased degree of point contact achieved between various points of thesurfaces of the two members and the additional fact that a greaterquantity of toner or powder can thus be carried to the image surface.Contrary to expectations, sliding contact seems not to cause smearing ofthe deposited image body. It is presently believed desirable to adjustthe relative motion of the members so as to bring a greater :area ofbelt 15 into contact with a lesser area of cylinder 41. Thus, it isgenerally desirable to operate belt 15 and cylinder 41 at differentspeeds with the motion generally being in the same direction and withbelt 15 traveling at a speed substantially greater than the speed oftravel of cylinder 41. Desirably, the belt may travel at a speedslightly in excess of the rate of travel over the cylinder, up to aspeed of as much as 5 to l0 times as fast as the travel of the cylinder.

At the transfer station, the image body deposited on the image surfaceat the development station is transferred to a print support member suchas a continuous roll of paper or the like to yield a xerographic printwhich desirably is made permanent by heat or vapor fusing or the like.As illustrated in Schaffert Patent 2,576,047, this transfer may beachieved by a corona discharge electrode of the same polarity as thecharging electrode 47. Other methods of transfer to 'a sticky surface orthe like are known to the art and are within the scope of the inventionas are other means or methods either obviating transfer or employingtransfer mechanisms of different types.

Leaving the transfer station member are two members, the transfer web 54bearing the powder image body corresponding to the pattern of light andshadow being recorded and the xerographic photosensitive surface whichmay bear a residual powder image and/ or residual electric chargeresulting from the previous steps of the operation. The photosensitivesurface is prepared again for renewal of the cycle of operations by suchcleaning or regeneration steps or techniques as may be desired. Amechanical cleaning operation to remove the residual powder images isspecifically disclosed in the figure but it is to be understood thatother mechanical or electrical preparation steps may be employed.

`Many modifications may be made without departing from the scope of theinvention. Thus, development may be carried out on a sheet or web,preferably a very good insulator, overlying an image-bearing surface asby passing web 54 of Fig. 6 between cylinder 41 and belt 15 or bysimilar modifications of the other figures. In view of these and othermodifications, the following examples are in illustration, notlimitation of the invention.

Example 1 A xerographic toner prepared in accordance with U.S. Patent2,659,670 and available under the name XeroX toner was employed as adeveloper material for a xerographic image consisting of anelectrostatic charge pattern corresponding to typed information. Thistoner Was placed on the surface of a bond paper by cascading over thepaper a mixture of this toner with a carrier composition as disclosed inWalkup U.S. 2,618,551. Several passes of developer mixture over thepaper were made until the paper was thoroughly covered with toner and asubstantially uniform coating of the toner was loosely adhering to thesurface of the paper. The powder-coated paper was placed on theimage-bearing surface with the powder coating face down, and the sheetwas pressed into contact with the image surface by means of a rubberroller which was passed lightly over the back surface. The sheet wasthen removed from the image surface and a deposit of powder in theconfiguration of the electrostatic image was observed on the imagesurface. This powder or image body was then transferred to a secondsheet of paper by conventional methods to yield a xerographic print.

Example 2 The procedure of Example 1 was repeated with the use of acoated or impregnated sheet prepared as follows. A 3% solution of zeinin 90% ethyl alcohol and 10% water was spread onto a base sheet of bondpaper. The solvent was evaporated at about 150 degrees F. in air untilthe sheet appeared fully dry.

The toner powder of Example 1 was applied to the surface of the thusprepared sheet by the same method, and the coated paper sheet was thenemployed as a developer member as in the previous example. In this case,it was observed that a slightly heavier powder deposit could be obtainedon the surface of the sheet and a substantially denser image body wasdeveloped on the imagebearing surface. The developer sheet memberlikewise was characterized by areas from which the powder deposit wassubstantially completely removed. These areas were corresponding to thedeposition areas on the imagebearing surface. The developer sheetmember, therefore, is a photographically negative copy of the completedxerographic print, which was formed on the image-bearing surface.

Example 3 The procedure of Example 1 was repeated with a sheet ofcellophane which was dusted with powder from a camels-hair brush to formthe developer member. Upon completion of the developing procedure therewas formed a developed image body on the image surface and a negativetransparency comprising the cellophane sheet and the residual oruntransfcrred powder thereon.

Example 4 The procedure of Example 1 was repeated employing a sheet ofbond paper dusted with toner powder. rl`his sheet was placed face downon a plate bearing a xerographic electrostatic latent image, and washeld in firm contact therewith by means of a weighted roller. The

developer sheet was removed from the image surface by a sliding actionin which the sheet was slid along the surface in one direction while theroller moved down the surface in an opposite direction, thus causingsliding contact between the developer sheet and the image surface. Thetoner particles were removed from the developer sheet in linescorresponding to image areas on the plate and a clear image of typedinformation was represented on the image-bearing surface by developer ortoner material removed from the developer member. The image body wastransferred to a second sheet of paper to yield a xerographic print ofsubstantially increased density with respect to the print of Example 1.Resolution in the deposited image was about 15 lines per millimeter, anddid not show substantial directional dilerence.

What is claimed is:

1. The method of developing an electrostatic image on an electrostaticimage-bearing member comprising forming a substantially uniform layer offinely-divided electrostatically charged powder marking particles on asmooth support surface extending across the image-bearing portion ofsaid image-bearing member, said particles loosely adhering to saidsurface by electrostatic attraction, contacting said image-bearingmember with said layer of marking particles, sliding said surfacebearing said layer of marking particles relative to said imagebearingmember and removing said surface from said image-bearing member wherebysaid marking particles are selectively transferred from said layer tosaid imagebearing member in the pattern of the electrostatic image.

2. The method of developing an electrostatic image on an electrostaticimage-bearing member comprising forming a substantially uniform layer offinely-divided electrostatically charged powder marking particles on aresin layer permanently bonded to a support surface extending across theimage-bearing portion of said imagebearing member, said markingparticles and said resin layer having a triboelectric relationship ofopposite polarity whereby said particles loosely adhere to said resinlayer by electrostatic attraction, contacting said imagebearing memberwith said layer of marking particles, sliding said surface bearing saidlayer of marking particles relative to said image-bearing member andremoving said surface from said image-bearing member whereby saidmarking particles are selectively transferred from said layer to saidimage-bearing member in the pattern of the electrostatic image.

3. In the method of developing an electrostatic image on anelectrostatic image-bearing member in which a substantially uniformlayer of finely-divided electrostatically charged powder markingparticles loosely adhering to a support surface by electrostaticattraction is brought into contact with the image-bearing surface of animage-bearing member and removing said support surface from saidimage-bearing surface whereby said marking particles are selectivelytransferred from said layer to said imagebearing member in the patternof the electrostatic image, the improvement consisting of sliding saidsupport surface bearing said layer of marking particles relative t0 saidimage-bearing member while said layer of marking particles contacts saidimage-bearing surface.

4. A method of developing an electrostatic image comprising forming anelectrostatically charged substantially uniform layer of finely-dividedpowder marking particles on a support sheet, said marking particlesadhering to said sheet by electrostatic attraction, positioning aninsulating film member in contact with the electrostatic image-bearingmember, contacting said insulating film member with said layer ofmarking particles while said film member contacts said image-bearingmember, sliding said surface bearing said layer of marking particlesrelative to said insulating film member and removing said surface fromcontact with said insulating lm member whereby said marking particlesare selectively transferred from said layer to said insulating lm memberin the member.

References Cited in the le of this patent UNITED STATES PATENTSHanington Feb. 14, 1928 Scott Dec. 16, 1930 Hay Mar. 31, 1936 CarlsonOct. 6, 1942 Carlson Sept. 12, 1944 Walkup et al Nov. 6, 1951 Sabel etal June 17, 1952 10 Walkup Nov. 18, 1952 Wise Nov. 18, 1952 Pethick Apr.7, 1953 Copely Nov. 17, 1953 Buttereld Nov. 2, 1954 Young et. al Jan.31, 1956 Greig Oct. 29, 1957 Clemens et a1 Apr. 1, 1958 FOREIGN PATENTSGreat Britain 1892 Great Britain Apr. 17, 1948

1. THE METHOD OF DEVELOPING AN ELECTROSTATIC IMAGE ON AN ELECTROSTATICIMAGE-BEARING MEMBER COMPRISING FORMING A SUBSTANTIALLY UNIFORM LAYER OFFINELY-DIVIDED ELECTROSTATICALLY CHARGED POWDER MARKING PARTICLES ON ASMOOTH SUPPORT SURFACE EXTENDING ACROSS THE IMAGE-BEARING PORTION OFSAID IMAGE-BEARING MEMBER, SAID PARTICLES LOOSELY ADHERING TO SAIDSURFACE BY ELECTROSTATIC ATTRACTION, CONTACTING SAID IMAGE-BEARINGMEMBER WITH SAID LAYER OF MARKING PARTICLES, SLIDING AND SURFACE BEARINGSAID LAYER OF MARKING PARTICLES RELATIVE TO SAID IMAGEBEARING MEMBER ANDREMOVING SAID SURFACE FROM SAID IMAGE-BEARING MEMBER WHEREBY SAIDMARKING PARTICLES ARE SELECTIVELY TRANSFERRED FROM SAID LAYER TO SAIDIMAGEBEARING MEWMBER IN THE PATTERN OF THE ELECTRISTATIC IMAGE.